US 20100228326 A1
Methods and apparatus for dermatology treatment are provided which involve the use of continuous wave (CW) radiation, preheating of the treatment volume, precooling, cooling during treatment and post-treatment cooling of the epidermis above the treatment volume, various beam focusing techniques to reduce scattering and/or other techniques for reducing the cost and/or increasing the efficacy of optical radiation for use in hair removal and other dermatological treatments. A number of embodiments are included for achieving the various objectives indicated above.
1. A photocosmetic device comprising:
a head adapted for applying radiation to skin, the head comprising a scanner configured to scan radiation in a direction substantially perpendicular to a direction of movement of the head as it is moved over the skin,
a motion sensor coupled to the head and adapted to generate one or more signals indicative of a rate of movement of the head as it is moved over the skin, and
controls coupled to the head for receiving said one or more signals and for controlling the rate of scanning in response to said one or more signals.
2. The photocosmetic device of
3. The photocosmetic device of
4. The photocosmetic device of
5. The photocosmetic device of
6. The photocosmetic device of
7. The photocosmetic device of
8. The photocosmetic device of
9. The photocosmetic device of
10. The photocosmetic device of
11. The photocosmetic device of
The present application is a continuation of U.S. application Ser. No. 11/437,434, filed May 19, 2006, entitled “Heads for Dermatology Treatment,” which is a continuation of U.S. application Ser. No. 10/274,582, filed Oct. 21, 2002, now issued as U.S. Pat. No. 7,077,840, entitled “Heads for Dermatology Treatment,” which is a continuation of U.S. application Ser. No. 09/634,981, filed Aug. 9, 2000, now issued as U.S. Pat. No. 6,511,475, entitled “Heads for Dermatology Treatment,” which is a continuation of U.S. application Ser. No. 09/078,055, filed May 13, 1998, now issued as U.S. Pat. No. 6,273,884, entitled “Method and Apparatus for Dermatology Treatment,” which claims the benefit of U.S. Provisional Application Nos. 60/046,542 filed May 15, 1997 and 60/077,726 filed Mar. 12, 1998. The entire contents of all above-listed applications are incorporated herein by reference in their entirety.
This invention relates to apparatus for using optical radiation to treat dermatological problems and, more particularly, to heads for such apparatus which heads provide an elongated focus area at a selected depth and/or selected preconditioning, for example heating and/or cooling, of a treatment area.
Lasers, lamps, and other sources of electromagnetic radiation, particularly in the optical wavebands, are being increasingly utilized for various dermatological treatments and, in particular, for the removal of unwanted hair, spider veins, leg veins, other veins or other blood vessels which are visible through the patient's skin, lesions, port-wine stains, tattoos, and the like. In performing such treatments, it is desirable that the cost for the treatment be kept as low as possible, consistent with achieving desired results, and that risk of injury to the patient be minimized.
Since continuous wave (CW) lasers and other CW radiation sources are typically substantially less expensive than pulsed sources of comparable wavelength and energy, for cost reasons, it would be preferable to use CW sources rather than pulsed sources for such dermatological treatments. However, in order to avoid injury to the patient, the duration of energy application to a given area of the patient's skin must be controlled, this generally resulting in the more expensive pulsed light sources being used for the various dermatological treatments. Further, since the only way to get radiation to areas where treatment is desired, which areas are normally in the dermis, is to transmit the radiation to such area through the overlying epidermis, some portion of incident radiation is absorbed in the epidermis creating the potential for damage thereto. This is a particular problem where melanin is being targeted in the dermis, as is for example the case for various hair removal treatments, since there is a substantial concentration of melanin in the lower portion of the epidermis at the dermal/epidermal (DE) junction. Further, the deeper in the dermis that treatment is desired, and/or the larger the element being treated, the more energy must be used, this generally involving the use of a more powerful laser or other radiation source and/or operating such source for longer time durations. This further increases the potential for epidermal damage.
Some attempts have been made in the past to scan a CW radiation source, such as the laser, over a treatment area, which has been done with the radiation source spaced from the skin in order to facilitate movement of the source. However, techniques currently utilized for protecting the epidermis frequently involve contact cooling of the epidermis and, for certain treatments such as hair removal, performing the treatment with pressure applied to the patient's skin is also desirable. Irradiation by use of a head in contact with the skin also permits more efficient transfer of energy into the patient's skin, thereby reducing the size of the source required for a given treatment energy density and, therefore, reducing the cost of such source. This cost could be further reduced if the radiation source is not the only source being utilized to heat the area under treatment.
Another problem in performing laser dermatology treatments, particularly when such treatment is to be performed over an area larger than the optical aperture of the applicator being utilized, is to obtain substantially uniform irradiation over the area so that sufficient radiation is applied to all portions of the area to achieve the desired treatment, while no portion of the area has so much radiation applied thereto as to cause thermal damage to the skin. Such uniform irradiation is very difficult with a pulsed source which typically utilize a circular aperture. Typically, the procedure followed is to irradiate a spot with a given pulse and to then reposition the head to an adjacent spot for irradiation. If the spots do not overlap, there will be portions of the area under treatment which do not receive radiation and, unfortunately, the radiation output is frequently not uniform over the entire optical aperture, being greater near the center, and less at the edges. Therefore, there is generally some overlap between adjacent spots. However, this results in some portions of the area under treatment receiving at least a double dose of radiation, which poses a potential danger of thermal damage in these overlap areas. Substantially uniform irradiation of a treatment area is therefore virtually impossible with a pulsed radiation source utilizing existing techniques.
Another problem which increases the energy required from the radiation source utilized is that, for existing systems, heating of the target to achieve the desired therapeutic effect is accomplished solely by radiation from the radiation source. If the temperature of the target could be increased by some type of preheating of the target volume, the amount of energy required from the radiation source to complete the job would be substantially reduced. However, such preheating must be achieved in a way such that the cost of such preheating is not greater than the savings achieved by reduced requirements on the radiation source.
Similarly, in order to protect the epidermis, many procedures require that the epidermis be cooled, preferably to the DE junction, to at least a selected temperature, for example 10° C., 0° C., or even slightly lower, before radiation is applied. If contact cooling starts when the head is over the target area, this means that there is some delay, perhaps half a second to a second, between the time the head is applied to the patient's skin and the time the radiation source is fired. With CW, such a delay once the radiation source is over the target area is difficult to achieve and it is therefore preferable that precooling of the epidermis occur for the target area before the radiation source is thereover. An ideal procedure would be to preheat the skin down to the target depth and then to precool to the DE junction, leaving the target depth preheated. Mechanisms in general, and heads in particular, for achieving such precooling and/or preheating followed by precooling have not heretofore existed.
It is also desirable to be able to focus the optical radiation at substantially the target depth. While heads have heretofore existed which are capable of achieving such a focus on a given spot, faster operation, particularly when operating in CW mode, although also when operating in pulse mode under some circumstances, can be achieved if there is a line focus at the target depth rather than a point focus. Mechanisms for achieving such a line focus have also not heretofore existed.
A need therefore exists for improved apparatus for utilizing optical radiation to treat various dermatological conditions, and in particular, improved heads for use in such apparatus which facilitate preheating and/or precooling of the target area, particularly when operating in CW mode, but also when operating in other modes, and which also facilitate achieving of a line focus for the radiation at a selected target depth for enhanced, and in particular, more rapid treatment.
In accordance with the above, this invention provides various heads for use in apparatus for effecting a selected dermatologic treatment in an area of a patient's skin. For some embodiments, the head includes a block formed of a material having good thermal transfer properties, a plurality of first optical waveguide elements and a plurality of second optical waveguide elements extending through the block, the first and second optical waveguide elements being angled at first and second angles respectively, which angles are selected so that light passing through the first and second optical waveguide elements converge at a selected depth. The optical waveguide elements have radiation applied thereto which is appropriate for the selected dermatologic treatment. The selected depth is in the area under treatment at which the dermatologic treatment is to occur. For some embodiments, a recess is formed in a surface of the head in contact with the patient's skin, the recess being at the distal end of the optical waveguide elements, and the selected depth is at a selected location in the recess. For these embodiments, a means is provided for moving skin in the area under treatment into said recess as said recess passes thereover. This means may, for example, include a source of negative pressure connected to the recess. For preferred embodiments, the block also has a skin contacting surface which retroreflects radiation leaving the patient's skin. A mechanism may also be provided for controlling the temperature of either the entire block or selected portions thereof.
For other embodiments, the head includes an astigmatic lens having an elongated outer surface, one side of said surface contacting the patient's skin in the area to be treated along an elongated line. A mechanism is provided which delivers light of a wavelength suitable for the dermatologic procedure to the lens on a side thereof other than the side contacting the patient's skin, the lens focusing light delivered thereto to a selected depth in the patient's skin. The lens may be a cylindrical lens with a diameter such that light delivered thereto is focused to the selected depth, and may be mounted to be either stationary or rotating as the head is moved over a treatment area. For some embodiments, the lens is treated so as to normally have total internal reflection, the total internal reflection being broken at a surface of the lens in contact with the patient's skin. To achieve the desired focus, the radius of curvature of the cylindrical lens for some embodiments is less than or equal 10 mm. For some embodiments, the selected depth is that for a portion of a hair follicle responsible at least in part for hair growth, for example, the hair bulge or the hair bulb. The selected depth may, for example, be 1 mm to 5 mm.
The mechanism for delivering light to the lens may deliver light along a line substantially parallel to the elongated line contacting the patient's skin surface and/or may cause light to be delivered to the lens at a variety of angles. A cooling mechanism may also be available for the patient's skin before the lens makes contact with the skin and/or while the lens is in such contact, the cooling mechanism for some embodiments, including a mechanism for cooling the lens. For some embodiments, the lens focuses light at said selected depth to an astigmatic focus area having a long dimension substantially parallel to the elongated line of lens contact with the skin. Finally, for some embodiments, the mechanism delivering light to the lens scans along the lens in its elongated direction, the scanning being at a selected rate.
More generally, the invention includes a focusing element having a light receiving region, a light delivery region which is adapted to be in contact with the patient's skin and a region which focuses light entering at said receiving region, the focus, when such element is in contact with the patient's skin being to an elongated astigmatic focus area at a selected skin depth. A mechanism is included which delivers light of a wavelength suitable for the dermatologic procedure to the light receiving region. The selected depth for some embodiments is the depth for a portion of a hair follicle responsible at least in part for hair growth, for example the hair bulge and/or hair bulb, and may be approximately 1 mm to 5 mm into the skin. A cooling mechanism for the patient's skin may also be provided, which mechanism is operated before the element makes contact with the skin and/or while the element is in contact therewith.
In accordance with still another embodiment of the invention, the head includes an optically transparent channel for delivering optical radiation of a wavelength appropriate for effecting the treatment in the area, a head portion of a thermally conductive material mounted relative to the channel so that it moves over each segment to be treated of such area before the channel, and a thermal component which controls the temperature of the head portion, and thus of each skin segment prior to treatment. In particular, the component may cool the portion, and thus each skin segment prior to treatment and/or the component may heat the portion, and thus heat each segment prior to treatment. The head may include a block formed of a material having good heat transfer properties, the block being adapted to move over the area during treatment, the channel being formed through the block and the portion being a portion of the block which is forward of the channel as the block is moved over the area. The head portion forward of the channel may be divided into a first thermally conductive portion which is heated and a second thermally conductive portion which is cooled, which portions are thermally insulated from each other, the first portion heating the patient's skin to the depth where treatment is to be performed and the second portion then cooling the patient's epidermis prior to irradiation. The head may also include a portion of a thermally conductive material mounted relative to the channel so that it moves over each segment to be treated of the area after the channel; and a thermal component which cools such rear head portion, and thus each skin segment after treatment.
While for preferred embodiments, preheating of the skin in the treatment area is accomplished in conjunction with the use of CW radiation and movement of the head over the treatment area, this is not a limitation on the invention, and preheating of the treatment area is also advantageous when employed with a pulsed radiation source. For such applications, preheating could be achieved by heating the waveguide or the portion of the head in contact with the segment under treatment prior to treatment to heat the skin down to at least to the depth where treatment is desired to a temperature which temperature is below that at which thermal damage occurs; and to then cool the surface in contact with the epidermis to cool the epidermis before irradiation begins. This results in the area under treatment having an elevated temperature when irradiation begins, thereby reducing the energy required from the radiation source. Alternatively, a low energy radiation source, which can be either the same or different than that used for treatment, can be used to perform the preheating operation.
The foregoing and other objects, features and advantages of the invention will be apparent in the following more particular description of preferred embodiments of the invention as illustrated in the accompanying drawings.
The apparatus of this invention includes an applicator 22 which may be mechanically driven, but which, for purposes of the following discussion, will be assumed to be hand operated (i.e., translated over the skin surface by hand). Applicator 22 includes a head 24 in contact with the patient's skin in the treatment area and a handle 26 which may be grasped by an operator to move head 24 in for example direction 28 across the patient's skin while preferably maintaining contact between head 24 and the patient's skin. Such contact should be under sufficient pressure between the surface of the head and the skin surface so as to, for preferred embodiments, assure good thermal and optical contact therebetween. Such pressure can be achieved by pressing the head against the skin, by using negative pressure to press the skin against the head or some combination of the two.
For some embodiments of the invention, a source of optical radiation 30 is connected to a light pipe 32, which for the embodiment of
Before discussing specific embodiments for head 24 and the manner in which the system of
Handpiece 24A has three sections, an optical channel 50 which is shown in
Sections 52 and 54 are each formed of a metal or other material having good thermal conduction properties. Sections 52 and 54 may be formed as a single block of a single material, with optical channel 50 being formed in the block, or, where sections 52 and 54 are to have different temperature profiles, the sections may, as will be discussed later, be two separate sections of the same or different materials secured together with a layer of thermal insulation therebetween. In
For the embodiment of
or pre-cooling, is roughly directly proportional to L1 and inversely proportional to V. Thus,
Since the time it takes for a temperature wave to penetrate to a depth z in the skin is, where α is the skin thermal-diffusion coefficient (α≈1.5·10−3 cm2/s). Therefore if these two times (T1 and T2) are roughly equal, then:
and the desired thermal effect will reach a desired depth z during the period that section 52 overlies the skin segment. Thus, L1 and V can be selected so as to achieve the desired thermal effect at a desired depth in the skin prior to irradiation. Since, as will be discussed shortly, V is also a factor in determining the duration of irradiation for achieving the desired therapeutic effect, L1 may be the prime factor in determining the depth for the desired thermal effect. For pre-heating, the depth z is the depth of the volume at which treatment is desired. For example, referring to
The temperature profile at the depth z is a function of the initial temperature of the skin and of the temperature of the section 52, 58 for head 24B. The length of the segment L1 and scanning velocity V are also factors in determining the final temperature at depth z. An estimate of skin temperature at depth z can be made using Thomson's equation as follows:
where T0 is the initial temperature of the skin, T1 is the initial temperature of the segment which is assumed for purposes of the equation to be segment 52. For scanning velocities in the range of approximately 0.05 to 10 cm/s, and length L of approximately 0.125 cm, desired pre-heating to a temperature in the range of +40° C. to +60° C. or pre-cooling of −30° C. to +20° C. can be achieved. Typically, the epidermis would be cooled to the DE junction to a temperature in the −5° C. to 0° C. range. Scanning velocities up to 10 cm/s should be achievable with contact scanning, but scanning velocities in excess of 10 cm/s may be more difficult to achieve.
The embodiment of
Radiation passing through waveguide or other optically transparent component 50 is directed through the epidermis, which has preferably been pre-cooled to the target, which may have been pre-heated, in order to achieve the desired therapeutic effect. In determining the time during which the target is irradiated, account must be taken of the fact that, due to scattering in the patient's skin, the beam width at the target can be greater than L2, the width of radiation at the skin surface, by a value Δ. Value L2+Δ can be minimized by focusing of the beam. Thus, the exposure time T2 of the target to CW radiation is given as,
The target has a thermal relaxation time which is generally a function of its size and of its shape. It is generally desirable that the time T2 be roughly equal to the thermal relaxation time of the target, assuming destruction of the target is the desired therapeutic effect, since this results in maximum heating of the target with minimal heating of surrounding tissue. In applications such as hair removal, where it has been found that some damage to a small layer of tissue surrounding the follicle facilitates permanent, or at least more permanent, hair removal, it may be desirable for the time T2 to be slightly greater than the thermal relaxation time of the target. In any event, for a target having a size or diameter d, the critical velocity at which dwell time on the target is roughly equal to its thermal relaxation time is given by,
where g is shape factor (g=8, 16 and 24 for stratified, cylindrical and spherical targets, respectively). Thus, where bulb 18 of a follicle is the target, g would be approximately 24. Assuming a maximum scanning velocity of 10 cm/s, and also assuming a depth z≈3 mm and L2+Δ of about 3 mm, equation (6) suggests that the process works best for stratified targets like fat layer with a thickness greater than 190 μm, cylindrical targets like a blood vessel with a diameter greater than 270 μm, and spherical targets like a hair bulb with a diameter greater than 320 μm. However, since, as discussed earlier, lower velocities would typically be employed in order to achieve pre-heating and/or pre-cooling for section 52, 58, significantly larger minimum target volumes are required for the various shapes in a practical system. However, since Vc is only a guide, and times less than or greater than thermal relaxation time of the target may be appropriate in some treatments, treatable target sizes will also vary. Effective pre-heating of the target may also reduce the required dwell time to achieve a desired therapeutic effect.
Another concern when employing the teachings of this invention for dermatologic treatment is that the temperature rise at the target be sufficient to achieve the desired effect. Where the treatment being performed is hair removal utilizing techniques similar to those described in U.S. Pat. No. 5,735,844 issued Apr. 7, 1998, it is necessary to heat the hair bulb to a temperature of approximately 65° C. to 75° C. The maximum temperature of a hair bulb undergoing irradiation is given by the following equation,
where, z is the depth of the bulb 18 in the skin T0 is the initial temperature of the bulb before irradiation a is the size of the irradiate zone inside the skin along the scanning direction at the depth z (as previously indicated a=L2+Δ) c and ρ are the heat-capacity and density of the bulb respectively k(λ) is the absorbing ability of the hair bulb and shaft defined by a concentration and a type of melanin, and depends on wavelength (is greater for dark hair and less for lighter hair) ψ(z, λ) is the radiance inside the skin at the depth z, caused by a light flux of unit power per length. It depends on both scattering and absorption inside the skin P is the power per unit length (i.e., equal to the total power applied to the skin surface per width of the light beam in the direction perpendicular to the direction of scanning. P is in units of W/cm. τ(d)=d2/gα is a period of thermal relaxation, where d is a diameter of the bulb, g is as previously indicated equal to 24 for a hair bulb, and α is the thermal diffusion coefficient of the tissue around the bulb.
For the destruction of a hair bulb, λ is in a range of 600-1200 nm and is preferably in a range of 670-1100 nm. In this range, k(λ) varies from 1-0.1 and decreases with increasing wavelength. ψ(z, λ) in this range increases with wavelength because of the weakening of the skin scattering properties and decreases with depth. At a depth of 3-5 mm where a hair bulb in its anagen stage is typically locate, this value, which is sometimes referred to as radiance attenuation, is in the range of 0.1-0.5. This value may be significantly increased where focusing techniques to be described later are used. With focusing, the reflection coefficient of light from the skin can be 20%-70%. Further, reflection of light scattered from the skin back into it by various means to be described increases the radiance in the zone of the hair bulge or in a hair bulb 1.2-2.5 times. Thus, the devices of this invention can allow ψ(z, λ) to be increased to 0.5-1.
From the above, it can be seen that, once the geometry of the systems has been selected, the temperature at the bulb is directly proportional to the applied power P and is
inversely proportional to the velocity V in a more complex way.
When the scanning velocity exceeds
When V is less than Vm, the average temperature of the hair bulb does not change with changing velocity, but selectivity of thermal damage decreases. Thus, by decreasing the velocity of scanning, it is possible to increase the diameter of the zone of thermal damage around the hair bulb. Maximum scanning velocity depends on the hair bulb dimension and decreases as the size of the follicle increases.
Thus, for hair removal, and regardless of the embodiment utilized, the following parameters would apply:
1. Wavelength: 600-1200 nm;
2. average power per length unit: 5-150 W/cm;
3. width of beam along direction of scanning: 0.05-5 mm;
4. scanning velocity: 0.01-10 cm/s;
5. temperature of cooling: −20° C.-+30° C.
For preferred embodiments, optically transparent section 50 is also cooled by thermal element(s) 56 b so as to prevent, or at least limit, heating of epidermis 12 in the treatment area during irradiation. This cooling effect is also a function of the scanning velocity and is particularly critical where irradiation used is of a wavelength which preferentially targets melanin, as is for example the case for certain hair removal treatments. Since there is a high concentration of melanin at DE junction 16, it is desirable that V be slow enough so as to permit heat produced at the DE junction to be removed through the cooled waveguide or other cooled optically transparent element 50. The maximum scanning velocity at which the cooling effect becomes noticeable for a given depth z is given by,
Where epidermis 12 to be cooled has a thickness of approximately 100 μm and the length L2 is approximately 1 mm, Vmax=6 cm/s.
Further, as indicated earlier, the pressure applied to the skin by head 24 in general, and by the skin-contacting surface of element 50 in particular, has a number of advantages, including improving the optical transmission (i.e., reducing scattering) for radiation passing through the skin. The head moving in the direction 28 over area 10 of the skin also stretches the skin in the direction of scanning resulting in an additional increase in skin transmission and thus the depth of electromagnetic wave penetration into the skin. Further, when the target is for example a hair follicle, the stretching of the skin turns the follicle to cause the radiation to impinge on a larger portion of the follicle and brings the follicle nearer to the skin surface.
Section 54 continues to cool the epidermis after irradiation to further guard against potential thermal damage to the skin. Unlike lengths L1, L2 and L4 which are fairly critical, the length L3 is not critical. The purpose of this section is to assure that the epidermis is not overheated and, if the prior sections are effective in keeping the epidermis temperature down, section 54 may not be required.
Since it is generally desirable to decrease the time element 50 is over the target, it is generally desirable that L2 be kept small. However, in order to achieve more rapid treatment, a significant beam aperture is desirable. This suggests that the dimension of the beam perpendicular to the direction of movement should be relatively large, resulting in an aperture for the skin contacting surface of element 50 which has an astigmatic shape, which shape may also be asymmetric.
Further, in order to deliver the radiation to a significant depth (i.e., greater than 1 mm) efficiently, large diameter beams are generally required to overcome the effect of scattering. With astigmatic beams of the type shown in
One problem with radiation treatments is that a significant percentage of the radiation applied to the skin is reflected back or backscattered by the skin and lost. Various schemes have been proposed in the past for retroreflecting such radiation back into the skin, including for example putting some type of reflector in section 50. Sections 52 and 54 might also have a reflective coating on their skin contacting surfaces to reflect such radiation back into the skin. Section 72 is particularly useful for this purpose since the entire skin-contacting surface 80 of this section may be formed of highly reflective material, or have a highly reflective coating formed thereon. By redirecting most of the radiation back into the skin, the intensity of radiation inside the skin can be increased 1.2 to 2.5 times.
While for the embodiments of the invention described so far radiation energy is applied in parallel along the length of the head during irradiation,
operates substantially the same as for previous embodiments. Again, for purposes of simplifying the drawings, elements such as thermal elements 56, motion sensor 78 and 102, and temperature sensors 94, are not shown in
While a number of embodiments and variations thereon have been described above, it is apparent that these embodiments are for purposes of illustration only and that numerous other variations are possible while practicing the teachings of this invention. For example, while in the discussion above it has been assumed that head 24 is manually moved over the treatment area, this is not a limitation on the invention and various types of mechanical scanners could also be utilized, either alone or in conjunction with manual control. Further, while optical and kinematic movement measuring mechanisms have been shown, suitable thermal, electronic and magnetic
movement measure mechanisms could also be used. Controls 34 would function to maintain the required scan velocity for such scanner. Thus, while the invention has been particularly shown and described above with reference to preferred embodiments, the foregoing and other changes in form and detail may be made therein by one skilled in the art without departing from the spirit and scope of the invention which is to be defined only by the appended claims.